Fiber optic strain twin-sensor-array for smart structural health monitoring

A multiplexed white light interferometric fiber optic twin-sensor-array was designed to monitor the structural health of large buildings.In this sensing system,based on a Michelson interferometer,an optical path matching technique is used to demodulate each twin-sensor.Each twin-sensor-array consists of a 2×N sensing element linked by a 3 dB coupler.When one of the twin-sensor is used to measure strain,variations caused by temperature can be compensated for by referencing the other twin-sensor.The multiplexing capacity of the sensing scheme has been analyzed and experimental results with a 2×3 twin-sensor-array are given.

Modeling, Simulation and Experimental Studies of Refractometric Fiber Optic Sensor

Refractometric fiber optic sensors have a number of applications in industry due to advantages like remote sensing ability, compact size, easy to fit, etc. A refractometric sensor contains a pair of parallel fibers and a gap between the sensor probe and reflector, wherein the liquid whose refractive index is to be measured is filled. This paper describes the importance of mathematical modeling of this sensor. Ray tracing approach is used to model the sensor mathematically. This mathematical model is generalized for any scenario which is useful to avoid tedious trial and error techniques to design the sensor prototype. Mathematical modelling is a useful tool to optimize the gap distance for a detection of refractive index of liquid. The model is developed and analyzed rigorously considering adulteration of diesel by kerosene where refractive index varies from 1.44 to 1.46. Simulation experiments are carried out to optimize the gap distance which is found to be 6.8 mm using both models. Experiments are carried out where sensor probe is fabricated and results are analyzed. It is observed that for suggested gap distance sensor output varies almost linear over the entire range.

A new demodulation technique for optical fiber interferometric sensors with[3×3]directional couplers

Optical fiber interferometric sensors based on [3×3] couplers have been used in many fields. A new technique is proposed to demodulate output signals of this kind of sensors. The technique recovers the signal of interest by fitting coefficients of elliptic （Lissajous） curves between each fiber pair. Different from other approaches, this technique eliminates the dependence on the idealization of [3×3] coupler, provides enhanced tolerance to the variance of photoelectric converters, and is anti-polarization in a certain extent. The main algorithm has been successfully demonstrated both by numerical simulation and experimental result.

Pulse reference-based compensation technique for intensity-modulated optical fiber sensors

We propose a compensation technique based on pulse reference for intensity-modulated optical fiber sensors that can compensate the power fluctuation of the light source, the change of optical components transmission loss, and the coupler splitting ratio. The theoretical principle of this compensation technique is analyzed and a temperature sensor based on fiber coating-covered optical microfiber is carried out to demonstrate the compensation effect. The system noise is measured to be 0.0005 dB with the temperature sensitivity reaching -0.063 dB/℃, and the output drift is 0.006 dB in 2 h at room temperature. The output shows a slight variation （0.0061 dB） when the light source and the common liKht path suffer a 3 dB attenuation fluctuation.

Recent advances in optical fiber high-temperature sensors and encapsulation technique[Invited]

In the aerospace field,for aerospace engines and other high-end manufacturing equipment working in extreme environments,like ultrahigh temperatures,high pressure,and high-speed airflow,in situ temperature measurement is of great importance for improving the structure design and achieving the health monitoring and the fault diagnosis of critical parts.Optical fiber sensors have the advantages of small size,easy design,corrosion resistance,anti-electromagnetic interference,and the ability to achieve distributed or quasi-distributed sensing and have broad application prospects for temperature sensing in extreme environments.In this review,first,we introduce the current research status of fiber Bragg grating-type and Fabry–Perot interferometer-type high-temperature sensors.Then we review the optical fiber hightemperature sensor encapsulation techniques,including tubular encapsulation,substrate encapsulation,and metalembedded encapsulation,and discuss the extreme environmental adaptability of different encapsulation structures.Finally,the critical technological issues that need to be solved for the application of optical fiber sensors in extreme environments are discussed.

An optical sensor for hydrogen sulfide detection in open path using WMS-2f/1f technique

An optical hydrogen sulfide(H_2S) sensor based on wavelength modulation spectroscopy with the second harmonic(2f) corrected by the first harmonic(1f) signal(WMS-2f/1f) is developed using a distributed feedback(DFB) laser emitting at 1.578 μm and a homemade gas cell with 1-m-long optical path length. The novel sensor is constructed by an electrical cabinet and an optical reflecting and receiving end. The DFB laser is employed for targeting a strong H_2S line at 6 336.62 cm^(-1) in the fundamental absorption band of H_2S. The sensor performance, including the minimum detection limit and the stability, can be improved by reducing the laser intensity drift and common mode noise by means of the WMS-2f/1f technique. The experimental results indicate that the linearity and response time of the sensor are 0.999 26 and 6 s(in concentration range of 15.2—45.6 mg/m^3), respectively. The maximum relative deviation for continuous detection(60 min) of 30.4 mg/m^3 H_2S is 0.48% and the minimum detection limit obtained by Allan variance is 79 μg/m^3 with optimal integration time of 32 s. The optical H_2S sensor can be applied to environmental monitoring and industrial production, and it has significance for real-time online detection in many fields.

Low-noise and highly stable optical fiber temperature sensor using modified pulse-reference-based compensation technique

We modify the pulse-reference-based compensation technique and propose a low-noise and highly stable optical fiber temperature sensor based on a zinc telluride film-coated fiber tip. The system noise is measured to be 0.0005 dB, which makes it possible for the detection of the minor reflectivity change of the film at different temperatures. The temperature sensitivity is 0.0034 d B/℃, so the resolution can achieve 0.2℃. The maximum difference of the temperature output values of the sensor at 20℃ at different points in time is 0.39℃. The low cost, ultra-small size, high stability, and good repeatability of the sensor make it a promising temperature sensing device for practical application.

Reflective Ladder Topology Network Based on White Light Fiber-Optic Mach-Zehnder Interferometer

In order to improve the multiplexing capability of the optical sensors based on the lower interferential optic fiber sensing technology and the white light fiber-optic Mach-Zehnder interferometer,reflective ladder topology network ( RLT) with tailored formula was proposed. The topology network consists of 6 rungs sensing elements linked by 5 couplers. Two cases with different choices of couplers were contrasted: one is equal coupling ratio,and the other is tailored coupling ratio. Through the simulation of these two cases,the detailed multiplexing capability was analyzed,and accordingly the experiments were also carried out. The simulation results showed that,the tailored formula enhances the multiplexing capability of the structure. In the first case, the maximum number of sensors which can be multiplexed is 8,and in the other case is 12 fiber optic sensors. The experimental results have a good agreement with numerical simulation results. Thus,it is considered expedient to incorporate RLT into large-scale building,grounds,bridges,dams,tunnels,highways and perimeter security.

基于光纤复合测量技术的涡轮叶片气膜孔检测

为了解决航空发动机涡轮叶片气膜孔几何特征参数有效检测手段缺乏、测量结果一致性差的问题,设计并搭建了基于光纤复合测量技术的涡轮叶片气膜孔检测系统,提出了利用该系统对涡轮叶片气膜孔进行测量的方法,通过试验进行了方法验证。搭建的系统为多传感器测量系统,具备叶片接触与非接触测量、空间姿态定位及3D投影能力,实现了涡轮叶片全范围气模孔的测量。在试验中,选取高压涡轮叶片作为被测物体,应用该测量系统对叶片上的气膜孔进行了测量,计算得到了气膜孔直径、轴线角度及位置度的准确信息。结果表明:通过测量不确定度的分析评定可知,该系统对气膜孔直径、位置度的测量不确定度均小于0.01 mm,完全满足设计公差对测量仪器的精度要求,可以用于涡轮叶片气膜孔工程化测量。

分布式光纤管道泄漏检测和定位技术

提出了一种基于Mach-Zehnder光纤干涉仪原理的新型分布式光纤管道泄漏测试技术。该检测技术利用在管道沿线附近敷设的一条光缆中的3条单膜光纤构成分布式微振动测试传感器,通过检测管道沿途所发生的泄漏噪声,可以实时地监测管道沿线所发生的泄漏情况。利用广义相关时延估计算法,通过确定2个测试信号的时延可以获得泄漏点的位置。阐述了该检测技术的测试原理和泄漏点定位方法,并对现场试验数据进行了分析。理论分析和试验结果表明,该测试技术可以有效地提高管道泄漏测试的灵敏度和定位精度。

线结构光测量技术研究进展

线结构光传感器由线激光器和相机组成,通过分析拍摄的调制光条图像获得被测对象的轮廓数据,具有结构简单、成本低、非接触、效率高、使用灵活等优点,在科研和工业生产中具有广泛的应用前景。从光条图像质量控制及中心提取、传感器标定、多个线结构光传感器协同测量、传感器和运动坐标轴结合4个方面对线结构光测量技术进行了综述,概括了目前线结构光测量技术研究和应用中存在的问题,并指出进一步提升测量精度、增强测量的适应性,以及研制基于线结构光传感器的智能测量系统是线结构光测量技术未来的研究方向。

双弹簧管光纤差压传感器

设计了一种利用对称反转连接的双弹簧管作为差动压力传感元件 ,进行差动压力测量的光纤传感器 这种光纤传感器是在通用光纤传感设计实验系统的基础上 ,利用三光纤反射调制技术 ,实现光源强度的变化和光纤中光功率损耗的变化以及反射率的变化自动补偿的 理论上 ,分析了这种反转对称差压传感弹性元件在使用过程的优点 ,给出了三光纤补偿理论分析方法 实验上 。

谐振式微型光学陀螺锁频精度分析

在谐振式微型光学陀螺(R-MOG)系统中,为了减小由I控制器取代一阶惯性反馈环节,建立反馈控制模型,对比分析PI控制器和一阶惯性反馈环节2种反馈方式对锁于光学器件受温度、应力等外界环境因素影响产生的各种噪声,提高环路锁频精度,在反馈回路中引入P频精度的影响.利用PI控制器设置的反馈回路能够消除环路的阶跃响应稳态误差,从而降低温度等外界因素引起的环形腔互易性噪声的影响,提高环路锁频精度.进一步优化PI控制器参数,将优化设计的PI控制器应用于R-MOG系统,得到锁定环路阈值精度为30Hz,对应环长为7.9cm的微型环形腔可检测转动角速度为0.15°/s,并在该芯片构成的系统上观察到20°/s的陀螺响应.

风力发电中全光纤风速传感器及制作工艺研究

为了实现风力发电场多点、远程风速检测,便于测量和风场风速物联网的构建,采用风杯来调制光纤布喇格光栅的方式,设计了一种全光纤风速传感器,通过光纤光栅波长的变化频率可以求出对应风速值,并对传感器设计结构进行了说明,介绍了传感器的制作封装工艺以及相关的设备和实验数据。结果表明,传感器运行稳定可靠,测量误差不超过0.16m/s,适合于风电场的多点大容量风速监测,对风力发电实际应用具有重大意义。

一种温度补偿式光纤氢气检测技术

基于非本征法布里-珀罗光纤传感检测技术,分析研究了氢敏薄膜特性,实现了氢气传感单元设计及制作,简要介绍了传感器结构、制作方法、镀膜工艺及设备。通过分析氢气浓度与法布里-珀罗腔长变化间的关系,建立了光纤法布里-珀罗氢气传感理论模型。为增强系统工程实用性,着重研究了传感器温度与氢气浓度交叉敏感问题,并利用温度补偿技术消除环境温度干扰。介绍了温度补偿原理并构建实验设备,最后通过氢气浓度响应实验及温度特性实验,证明理论公式推导结果与实验数据吻合较好,且氢气传感器温度敏感性降低。此设计具有一定工程实用价值。

基于法拉第效应双偏振光纤激光磁场传感器的纵向空间响应

利用法拉第效应,正交双偏振光纤激光器已被证明可用来实现灵活小巧的磁场传感器.为了发展适宜的封装结构以优化对磁场的传感灵敏度,有必要研究双偏振光纤激光磁场传感器在磁场中的空间响应特性。对长度为21 mm的光纤激光器在磁场宽度为3 mm、5 mm、7 mm以及磁场强度为0.5 T、0.75 T和1 T时的纵向空间响应进行了实验研究。研究表明,沿着双偏振光纤激光磁场传感器的纵向,其各个部分对磁场的空间响应是不均匀的。空间响应的峰值出现在激光腔的中间并沿激光器纵向呈对称的高斯分布。这种空间响应的分布特性与光纤光栅的分布式布拉格反射有关。

基于ART的光学过程层析成像扇束图像重建

光学过程层析成像是近几年发展起来的一种新型的光学测量技术 ,它源于医学 CT的基本理论和方法 ,可认为是医学CT技术在工业过程监测领域的自然延伸和发展。然而 ,由于过程层析成像的被测对象为快速变化的工业过程 ,因此 ,其投影数据的数量比医学 CT少得多 ,而实时性则要求更高。利用一种扇束扫描制式的光学传感器有利于提高光学过程层析成像的空间分辨率及测量精度 ,但在这种扫描制式下 ,引用医学 CT的常见图像重建算法 (如数据重排方法、反投影法和滤波反投影法等 )却不适用或难以胜任工业检测的要求。为此提出了一种代数重建技术来提高光学过程层析成像的测量精度和速度。该算法不仅适用于少数投影数据的情况 ,也能使求解过程遍历几乎所有的图像像元 ,因此成像效果好和实时性较高 。

基于光纤传感的富士苹果糖度检测试验研究

利用傅立叶光谱仪的智能光纤传感器 ,探讨了近红外光无损检测水果糖度的方法。通过主成分回归、偏最小二乘法和逐步回归法三种多元校正算法对水果光谱数据的分析 ,得出PLS模式水果糖度预测值和真实值的相关系数为 0 86 ,标准校正误差为 0 14 ,标准预测误差为 0 97,PCA模式水果糖度预测值和真实值相关系数为 0 85 ,标准校正误差为 0 4 7,标准预测误差为 1 2 7,而SMLR模式的水果糖度预测值和真实值相关系数为 0 72 ,标准校正误差为 0 72 ,标准预测误差为 2 10 ,研究结果表明 ,在 12 5 0 0～ 380 0cm- 1

干涉型光纤传感器及阵列的分集消偏振衰落技术的研究与改进

对干涉型光纤传感器的分集检测消偏振衰落技术进行了新的理论分析 ,提出了将各路信号平方后相加的信号处理方式 ,使之能实现单元及阵列的实时消偏振衰落信号检测 .通过理论计算 ,可以使干涉信号幅度波动小于 9.5d B,并得出三路检偏是分集检测的最简取值的结论 ,通过自动增益控制电路 ,能够在信噪比有所降低的情况下消除偏振衰落的影响 ,实现干涉型光纤传感器的消偏振衰落 。

基于光纤传感的边坡工程监测技术

传统的边坡监测技术存在着精度低、耐久性差、难以实现集成等缺陷。针对边坡工程特点,探讨了光纤光栅、布里渊光时域分析和低相干干涉等光纤传感技术在现场监测的应用。根据不同的工程需要,结合这三种技术建立边坡监测系统,可用于对边坡位移和边坡支护结构的应力、应变进行自动化监测。在详细论述了光纤传感技术的基本原理、适用场合和系统架构的基础上,以香港一个公路边坡加固工程为例,简述了光纤传感技术现场应用时的仪器安装、数据采集与分析等工作。